The Abel dashpot is introduced to improve the classical three-parameter Merchant model, and a fractional Merchant model which can better describe the viscoelastic characteristics of soils is obtained. With the help of finite element method, the pile group is discretized into single piles and pile elements. The total stiffness matrix equation of the pile group can be obtained by assembling the pile elements simulated by the Timoshenko beam model. According to the interaction equation between soils and the pile group, and the equilibrium condition and the compatibility condition of the pile cap, the matrix solution of the shear force at the top of the single pile and the displacement of the pile cap is deduced. Combined with the elastic-viscoelastic correspondence principle and the Laplace inverse transformation, the problem of the interaction between fractional viscoelastic saturated soils and laterally loaded pile groups is finally solved. Taking a set of creep test data as an example, this paper briefly introduces the specific method to obtain the viscoelastic parameters of the fractional model through the creep curve. The correctness of the proposed solution is verified by comparing with the published results and ABAQUS numerical examples. Additionally, several examples are designed to discuss the effects of soil’s viscoelasticity parameters on the stress and deformation of the pile group, which shows that with the development of soil’s rheology, the internal force gap between corner piles and central piles gradually shrinks and tends to be stable.

In order to accurately obtain the vertical and horizontal saturated permeability coefficient of undisturbed Q3 loess, in-situ tests, laboratory tests and numerical tests were carried out, and the reliability of the saturated permeability coefficient measurement was verified by large-scale test pit immersion test. Firstly, the in-situ double ring infiltration tests with different inner diameter sizes were carried out to obtain vertical saturation coefficients and indoor tests were applied to test vertical and horizontal saturation coefficients and water holding curve. Then, COMSOL software was used to simulate the double-ring infiltration tests, the optimal values of vertical and horizontal saturated permeability coefficients were obtained by orthogonal tests, and the inversion results were used to simulate the test pit immersion test, and the simulated water infiltration was compared with the measured values. The results show that the saturated permeability coefficient obtained by selecting the double-ring with larger inner diameter is more rational in the field double-ring infiltration test. For the double-ring infiltration test, the optimal vertical saturated permeability coefficient obtained by numerical simulation inversion is close to the vertical saturated permeability coefficient obtained by in-situ test in the vertical direction, and close to the horizontal saturated permeability coefficient measured in the laboratory in the horizontal direction. The vertical saturated permeability coefficient affects the water infiltration process more significantly than the horizontal saturated permeability coefficient. The reliability of the optimal saturation permeability coefficient obtained from the inversion was tested by verifying the water infiltration in a large test pit.

Slurry shield tunnelling method is widely used in the complex geological environment with high water pressure for tunnel construction. The face stability control is the key for the engineering safety during shield tunnelling. Due to the continuous rotation of the cutter head, the filter cake is in the "formation-destruction-re-formation" dynamic cycle process, resulting in a relative permeable membrane. How to evaluate face stability under this dynamic filter cake need to be further explored. In this paper, the dynamic filter cakes are divided into three types. An analytical approach is developed by coupling the penetration-filtering and shield movement. Based on the pressure transfer mechanism of the bentonite suspension, a new penetration-type model for the evaluation of face stability is developed. It can be found that the slurry viscosity as well as the filter cake ratio should be paid more attention during tunnelling in the high permeable ground. A faster advance rate and a lower rotation speed of the shield machine could improve the face stability. Finally, a design chart of slurry support efficiency is provided, which could give some reference for the control of support pressure and slurry selection in engineering practice.

Quasi-saturated clay is assumed to consist of saturated matrix (soil skeleton and water) and occluded gas. Plastic volumetric strain of saturated matrix and gas is used as hardening parameter to reflect the plastic hardening behavior of quasi-saturated clay. The variation of gas solubility coefficient with temperature and salinity in water and the variation of pre-consolidation stress with occluded gas are used as key factors. Based on the theory of critical state mechanics, an elastoplastic model is proposed to reflect the influence of the pressure change of the occluded gas on the mechanical characteristics of quasi-saturated clay. There are 10 material parameters in the proposed model, all of which can be obtained from compression test and triaxial shear test. By comparing against existing experimental data, the results show that the model can well simulate the stress-strain relationship, pore water pressure development and saturation evolution under undrained stress path. The proposed elastoplastic model is simple in form and its parameters can be easily determined, and it provides an important theoretical basis for the design, calculation and disaster control of geotechnical engineering problems in quasi-saturated clay foundations.

During the operation of underground repository of high-level radioactive waste, the highly alkaline solution generated by groundwater corroding lining concrete will diffuse into the bentonite buffer barrier, resulting in the degradation of barrier property. The KOH solution with different pH values was used to simulate the alkaline solution, and a one-year contact diffusion test at room temperature was conducted. Then, X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) were performed to investigate the effect of slow diffusion on the mineralogy of bentonite. The XRF test results show that when the pH of KOH solution was greater than 12.6, the content of silicon began to decrease, that is, montmorillonite, quartz, cristobalite and other Si-containing minerals in bentonite were dissolved. At the same time, the content of K increased, indicating that the bentonite had an ion exchange reaction with the alkaline solution, a large amount of K⁺ ions in the solution entered the montmorillonite crystal layer. The XRD test results show that the 001 peak of montmorillonite mineral started to shift to the right at pH=12.6, the peak widths widened, and the peak intensity reduced considerably. When the pH>13, the crystal interlayer space decreased from 1.385 3 nm (13.853 Å) to 1.221 0 nm (12.210 Å), indicating that the crystal layer of montmorillonite was compressed. With the increase of the pH value, the content of minerals such as montmorillonite and quartz decreased significantly, and the contents of illite, clinoptilolite and feldspar minerals increased slightly. The SEM test results show that part of the montmorillonite crystal layer overlapped with the pH of the solution increasing, and then some cracks and holes were generated. As a result, the cracks can accelerate the dissolution of montmorillonite. In the one-year contact diffusion test, the diffusion depth of the KOH solution with pH=13.8 exceeded 7.5 mm, and the newly formed illite crystallites were observed on the contact surface between the alkaline solution and the bentonite. It is confirmed that the strong alkaline solution will cause montmorillonite dissolution and illitization.

The concrete-granite combined body is a typical binary material in engineering, with mechanical response properties that differ from monomer under triaxial circumstances. Concrete monomer (CM), granite monomer (GM), and concrete-granite combination body (CGCB) were subjected to quasi-static compression tests under various confining pressures. To reveal the overall crack propagation and failure mechanism of the composite specimens, SEM was used to study the fracture and interface microstructure of CGCB, and RFPA was employed to simulate the failure process of CGCB. Finally, based on the Mohr-Coulomb strength criterion, a prediction model for composite triaxial compressive strength was developed. The results show that the uniaxial (triaxial) compressive strength of CGCB is affected by the material size effect and the interface constraint effect, and the failure condition of the combined body shifts from uniaxial "Y" splitting failure to shear failure of the concrete component when confining pressure is increased. Under various confining pressures, the concrete away from the contact and the granite near the interface are damaged in turn, and shear fractures occur progressively, resulting in the splitting failure of granite components, according to the numerical simulation findings. The strength prediction model can match experimental data and numerical simulations effectively, demonstrating the accuracy of the model. The findings of the study might serve as a scientific foundation for the excavation and support of deep subterranean engineering constructions.

In order to explore the damage characteristics of filled jointed rocks under dry-wet cycles in acidic environment, some experimental studies are carried out in the present study. Firstly, the prefabricated filled jointed rock samples are treated with different number of dry-wet cycles under acidic and neutral environments. Then, the uniaxial compression test and dynamic impact test are carried out by universal testing machine and split Hopkinson pressure bar (SHPB) device. Accordingly, the degradation effects of longitudinal wave velocity, static compressive strength and dynamic compressive strength of the filled jointed rock under the action of dry and wet cycles in acidic and neutral environments are analyzed. The results show that the wave velocity, static compressive strength, and dynamic compressive strength of the filled jointed rock continue to decrease, and the degree of deterioration continues to increase with the increase in the number of wet and dry cycles, whether in acidic or neutral environments. The static compressive strength deteriorates most obviously under acid dry-wet cycling. In addition, it is found that there are linear relationships between the static and dynamic compressive strengths and wave velocity values of the filled jointed rocks subjected to dry-wet cycles; the degree of pulverization of the joint filling layer and the degree of rock fragmentation on both sides are more serious under the dry-wet cycles in acidic environment. The research results can provide a scientific basis for the stability analysis of engineering rock mass under the action of dry-wet cycles in an acidic environment.

The impermeability of cement-stabilized silty sand is significantly affected by the permeability of itself, the dosage of cement, the water-cement ratio, and other factors. How to improve the impermeability of cement-stabilized silty sand while reducing cement dosage is the key to improving the economic benefit of the project. In this study, a series of indoor permeability tests was conducted on cement-metakaolin stabilized silty sands with different cement-metakaolin ratios, initial water consumption, total cement-metakaolin contents, and curing ages. The influence of the above factors on the impermeability of cement-metakaolin stabilized silty sands were investigated, and the empirical relationships between the permeability coefficient and these factors as well as their corresponding unconfined compressive strength were discussed. The results showed that the impermeability of cement-metakaolin stabilized silty sands achieved the optimization when the ratio of cement to metakaolin was 5:1, and this mixing ratio did not change with the total cement-metakaolin content used in silty sand stabilization. The permeability coefficient of cement-metakaolin stabilized silty sands increased nonlinearly with the initial water consumption and decreased rapidly first and then slowly with the increase of the total cement-metakaolin content and curing age. Four empirical formulas for the permeability coefficient of cement-metakaolin stabilized silty sands were summarized with respect to initial water consumption, total cement-metakaolin content, curing age, and unconfined compressive strength. The results of this study can provide a theoretical reference for improving the impermeability of cement-stabilized silty sands.

There exist coal seams of various ranks in China. Due to differences in coal quality and geological conditions, the occurrence of water in different coal seams is different. Coal rank and water saturation are two important factors affecting the cracking effect of liquid nitrogen at low temperature, which are worthy of further study. Therefore, three ranks of coals, including lignite, bituminous and anthracite coal samples, were chose to be treated as coal samples with 0%, 33% and 99% water saturation respectively for liquid nitrogen immersion. The camera was used to shoot and observe the variation of macroscopic cracks on the surface of coal samples before and after treatment. The coal sample was tested with nitrogen seepage. The experimental results were as follows. 1) The lignite after liquid nitrogen immersion was destroyed as a whole due to one and several penetrating cracks. New cracks were created on the surface of bituminous coal, and the original macroscopic cracks were expanded and extended compared with those before treatment. Macroscopic cracks on the surface of anthracite have no visible changes. 2) The higher the saturation of coal sample was, the better the fracturing and enhancing permeability effect of liquid nitrogen was. 3) The ranking of fracturing and enhancing permeability effect of liquid nitrogen immersion on three coal rank coal samples is as follows: lignite> bituminous coal> anthracite coal, but in the completely dry state, enhancing permeability effects of the bituminous coal and anthracite coal were approximately the same because the thermal stress was not enough to destroy the inter particle linkage. 4) Liquid nitrogen immersion could effectively crack the completely dry lignite, and the permeability of treated lignite increased by 559.35% on average. Liquid nitrogen immersion could significantly crack the bituminous coal with 33% and 99% water saturation, and the average increase of permeability of treated bituminous coal was 330.60% and 448.77%, respectively. For the anthracite with 33% and 99% water saturation, average permeability increase was 185.53%.

The plant-derived urease-induced calcium carbonate precipitation (EICP) can significantly improve the engineering mechanical properties of sand. However, there is no corresponding specification for the parameter value in the specific operation, and the reinforcement effect needs to be improved. Based on soybean urease, the effects of temperature, urease concentration, urea concentration, calcium concentration, pH, calcium source type and other variables on urease activity and calcium carbonate precipitation were studied, and the tests on SEM and XRD of precipitated calcium carbonate crystals were carried out. On this basis, the unconfined compressive strength and curing effect of soybean urease-cured sand were tested. The results showed that urease activity increased linearly with the increase of urease concentration, but there was a temperature threshold value. When the temperature exceeded the threshold, urease activity was completely inactivated, and the threshold decreased with the increase of urease concentration. Urea concentration and pH affected urease activity together, and there was an optimal combination of them, that is, the optimal pH is 7 when urea concentration is 0.1-1 mol/L, and it is 8 when urea concentration is1.0-1.5 mol/L. Urease is the catalyst of a precipitation reaction. The higher the urease concentration was, the more complete the reaction was, and the higher the precipitation rate of calcium carbonate was. For urea and calcium solution, the dosage mainly affected the precipitation of calcium carbonate, and the dosage ratio should be 1:1. The concentration and pH of urea and calcium solution can affect the precipitation of calcium carbonate by affecting urease activity. Different calcium sources had little influence on the precipitation amount of calcium carbonate. The composition and density of precipitated calcium carbonate crystals from different calcium sources were basically the same, but the crystal structure was very different. The calcium chloride precipitated calcium carbonate crystals are mainly massive, with spherical and spheroidal crystals on the surface and large cementation surface, which can be used as an ideal calcium source in EICP technology. The unconfined compressive strength of the sand solidified with urease from soya beans and calcium chloride as calcium source was about 6 times that of the sand mixed with coal fly ash. SEM images show that the precipitated calcium carbonate crystals wrap and bond the sand into a whole, and the curing effect is ideal.

The pick is the main load-bearing object of the mining machinery for cutting coal, and the prediction of the cutting force from the working face is very important to reduce the wear of the pick. The rock was considered as a particle matter for single pick cutting simulation by using the particle flow code (PFC2D). The influence of the contact state on the cutting force of the single pick was discussed by studying the characteristics of the interparticle force chain during cutting. The cutting force test was carried out on a single pick cutting rock test equipment, and the changing law of normal and tangential force with cutting parameters and the characteristics of falling fragments were obtained. The research results show that the relationship between the number of force chains and the length of the force chains for rock particles cut by a single pick is consistent with the uniaxial compression test results, and the cutting state of the single pick can be simulated by using discrete element method. The force chain network spreads and extends along the point contact direction, which is related to the cutting angle. The average normal force direction is "peanut"-like whereas the tangential force direction is "petal"-like. In addition, the number of force chains decreases with the decrease of cutting angle and the increase of cutting depth. The length of force chains increases with the increase of cutting distance. The maximum average length is about 8 particle sizes. The force chains tend to form at larger cutting angles. Furthermore, the normal force and tangential force of single pick cutting of natural sandstone decrease with the increase of cutting angle and the decrease of cutting depth. The linear correlation between the size of the cutting fragments and the cutting tangential force is 0.87. Compared with the Evans prediction model, the accuracy of normal force and tangential force based on force chain length is improved by 17.6% and 16.9% respectively. The research results lay a certain research foundation for the design of cutting pick, mining machinery cutting system and the optimization of cutting technology.

A series of 3D cyclic large-scale direct-shear tests of a gravel-structure interface was conducted at different stress amplitude ratios using 80 t 3D multifunction apparatus for soil-structure interface (3DMAS). The 3D cyclic interface behavior, including tangential deformation, non-coaxial angle and shear flexibility, was addressed in stress-controlled two-way elliptical shear path and the influence of stress amplitude ratio was discussed in detail. Distinct tangential displacements in the x and y directions, non-coaxial angle, shear flexibility are observed subjected to two-way elliptical cycling of shear stress. The tangential displacement amplitudes in the x and y directions and the shear flexibility of the interface gradually decrease with cyclic shearing and then tends to be stabilized, indicating noticeable evolution characteristics. The non-coaxial angle is significantly dependent on the shear stress amplitude and the shear stress increment direction, and the maximum, minimum and stabilized non-coaxial angles almost remain invariable throughout cyclic shearing. The development of the shear flexibility against rotation angle is contrary to that of the non-coaxial angle, and the rapid growth of the peak shear flexibility will impede the development of the non-coaxial angle of the interface. The stress amplitude ratio slightly influences the relationship patterns of the tangential displacements in the x and y directions and their relationship patterns against shear cycle, and the shear stress-displacement relationship patterns, but significantly affects the tangential displacement amplitudes and their migration extent, the length of the major and minor axis of the elliptical curves of the tangential displacements in the x and y directions and of the shear stress-displacement response, as well as the magnitude and development trend of the non-coaxial angle and shear flexibility. Increased stress amplitude ratio leads to magnified tangential displacement amplitudes and enlarged migration towards the negative direction, increased peak shear flexibility and slowed evolution with cyclic shearing. In addition, the non-coaxial angle and the shear flexibility present different performances when the stress amplitude ratio equals and does not equal 1.0.

Based on the 1g model tests, the uplift behavior of the double-blade screw anchor in loose sand was studied, where the influences of the embedment ratio and blade spacing were focused. Digital image correlation (DIC) was used in the half-model tests to analyze the deformation and failure mechanism of soils around the anchor during the uplift process. A theoretical formula for predicting the ultimate bearing capacity of double-blade screw anchors in loose sand was proposed based on the results of the half-model tests. The results show that the embedment ratio and blade spacing affect both the ultimate uplift bearing capacity and the displacement corresponding to the peak uplift force. For the double-blade screw anchors in loose sand, the embedment ratio H/D=3 can be regarded as the demarcation between shallow and deep anchors, where H is the embedded depth of the upper anchor blade, D is the diameter of the blade. When embedment ratio H/D3 is applied, the failure mode of soils above the upper blade gradually changes from overall shear failure to local shear failure. The spacing ratio S/D=2.5, where S is the blade spacing, can be regarded as the critical point that makes the failure of soils between two blades from the cylindrical shear failure to independent bearing failure. By comparing with the full-model tests and the experimental results in the literature, it is found that the prediction errors of the proposed theoretical formula for the ultimate uplift bearing capacity are generally within 25%. Thus, the reliability of the theoretical formula is verified.

The aim of this study is to investigate the feasibility of utilizing the waste plastic bottles filled with soil as the transverse element attached to the steel stripe in the Mechanically Stabilized Earth Walls (MSEWs). Transverse members of reinforcement have a major effect on increasing the pullout resistance. This system is comprised of a steel stripe as a longitudinal member and waste plastic bottles filled with soil as transverse members attached to it. To understand this, pullout tests were conducted on one steel strip and seven steel stripes with one to seven bottles. More than 18 laboratory large-scale pullout tests (i.e. length1.20 m, width 0.6 m, and height 1 m) under different normal stresses were conducted to evaluate the performance of the newly suggested reinforcement element. The results showed that creating a third dimension on a flat steel strip has a great effect on increasing the pullout resistance, the most efficient adding four transverse members to the steel strip with the ratio of distance to diameter (S/D) equal to 3, that the pullout resistance was to average about 5 times greater than the steel strip alone. The ultimate pullout resistance for steel strips with transverse members and without transverse members increased by increased vertical stress.

To explore the influence of tailings particle size distribution on strength and damage characteristics of filling body, uniaxial compression, scanning electron microscopy, and digital image correlation (DIC) tests were carried out on the filling body composed of ultrafine tailings (median particle size D₅₀=10.1 μ m), fine tailings (D₅₀=37.1 μ m), and coarse tailings (D₅₀= 121.31 μ m), and the strength and microstructure characteristics were analyzed. Based on the cusp mutation theory, the damage identification index of the filling body was established using wavelet packet technology, and the damage characteristics of the filling body were quantitatively analyzed. The results reveal that the strength and elastic modulus of the filling body first increase and then decrease with the increase of D₅₀, but the influence of tailings particle diameter on the strength and elastic modulus of the filling body is reduced with the increase of slurry concentration. Compared with the ultrafine and coarse tailings filling body, the coarse and fine particles of the fine tailings backfill are more closely combined, and its porosity is the lowest and microstructure compactness is the best. The energy change rate (ECR) mutation point is defined as the threshold of the backfill specimen damage mutation, which is used to distinguish the stable damage stage and the accelerated damage stage of the specimen, and the damage mutations of the ultrafine, fine, and coarse tailings filling body occur when their stresses reach 92.83%, 92.31%, and 72.93% of the corresponding peak stresses. With the increase of D₅₀, the failure mode of the backfill changes from shear failure to tensile failure, with the ECR increasing from 20.65% to 28.25%, and the damage degree is gradually aggravated. The research results lay the foundation for improving the particle gradation of mine tailings and enhancing the strength of filling body.

Suffusion is the main and prominent form of seepage stability in deep alluvium foundation. It is of great theoretical and practical significance to carry out relevant experiments and theoretical studies on suffusion in deep alluvium foundation for the safety of major hydropower projects under construction and to be built in China. In this paper, firstly, it is pointed out that the mechanisms of backward erosion piping and suffusion are completely different, so they cannot be confused together. Compared with backward erosion piping, suffusion is more subtle, and its mechanism is more complex. Secondly, the research of suffusion is summarized in detail from three aspects: geometric condition, hydraulic condition and mathematical model. Finally, combined with the lower Yarlung Tsangpo River hydropower development and other major national projects, the following aspects should be emphasized, including the evaluation of internal stability in deep alluvium foundation, the mechanism of suffusion initiation and progression under extreme conditions, complex seepage conditions and formation conditions, the evaluation and control of suffusion time effect and its long-term impact, and the experimental and theoretical research of suffusion constitutive relation and its mathematical model.

Resource recharge of groundwater extracted from dewatering project is an effective choice to protect groundwater resources in groundwater control of high permeability water-rich strata. When the recharge site is not far enough away from the dewatering affected area, there may be coupling effect between dewatering and recharge. Based on the phreatic line equation of fully penetrating well dewatering-recharge well group, the approximate theoretical solutions of equal flow rate and equivalent large well for integrated dewatering-recharge well point group system are derived, and the errors are analyzed. A foundation pit project in Beijing are analyzed as an example, and it is found that the results of the approximate theoretical solution, numerical modeling analysis and flow measurement of the integrated dewatering and recharge project are consistent with each other, which verifies the reliability of the formula. The solution idea and solution steps of the integrated dewatering and recharge design problem under site limited conditions by using the formula are given to establish the integrated dewatering and recharge design method of the complete phreatic well.

To comprehensively evaluate the pavement performance and the particle breaking behavior of carbonaceous shale, the gradation change of carbonaceous shale during cyclic compaction is tested. According to the indoor compaction test, the influence of particle breakage on filler is described, and the best filling gradation is determined. The best gradation is selected for the wetting deformation test, and the variation law of the wetting deformation is analyzed from the perspective of particle breakage. Finally, the field filling effect of carbonaceous shale is verified. Three stages, i.e., structure adjustment, particle breakage, and compression deformation, are identified during the cyclic compaction of carbonaceous shale. The relatively stable gradation structure formed provides the basis for its use as filler. The formation mechanism of the maximum dry density of fillers is greatly affected by the changes in the contents of 20-40 mm and below 2 mm particles during the particle crushing process. The relative breakage rate of the sample increases linearly with the increase of the coarse grain content, the maximum dry density increases first and then decreases, and the optimal coarse grain content is about 70%. The wetting deformation is the macro embodiment of the fillers particle crushing. The relative breakage rate Br can be used to predict the wetting deformation of fillers when encountering water, and the strength decreases by about 40% after wetting deformation. The mathematical relationships between the relative breakage rate and the confining pressure, stress level are established. The on-site compaction test and settlement observation show that the best loose paving thickness of carbonaceous shale embankment is about 40 cm.

The dynamic penetration index correction, test stability and relationship of blow-counts are closely related to the effective hammer impacting energy. Strain gauges and acceleration sensors were installed at the top of the probe rod and the probe, and the hammer energy of heavy and super-heavy dynamic penetration under different probe rod lengths was measured. The results show that when the single probe rod in the probe rod is short and there are many joints, the hammer energy of the probe rod calculated by the force square method (F2 method) with an integral domain of (0, 2l/c) differs greatly from the actual hammering energy, where l is probe rod length, c is wave velocity. Due to too many interference factors in the in-situ test, it is more reasonable to the force velocity method (FV method) that selects the first extreme value and the F2 method selects the time when the hammering axial force first passes through the zero point as the integral end time of hammering energy to calculate the hammering energy. As the length of the probe rod increases, the hammer energy reaching the probe decreases linearly. Blow-count converting coefficients for heavy and super-heavy hammer numbers under the rod lengths of 3, 5, 8 m, and 11 m are 2.285, 2.160, 2.440, and 2.810, respectively, which are basically consistent with the total potential energy ratio of super-heavy and heavy hammer.

To further improve accuracy and reliability of describing the roughness feature of the structural plane, and more comprehensively reflect influences of the morphological differences, the fluctuation of the profile was decomposed into three principal characteristics: amplitude, inclination, and curvature, which represent the change characteristics of height, angle, and bending of the profile. The data of the three characteristics were obtained by 10 standard profiles established by Barton. And the distribution curves of the three characteristics were analyzed. Then, the power spectral density (PSD), which can well describe the microscopic morphology, was used to analyze the spectral characteristics of amplitude, inclination and curvature. The fractal parameters D_j (corresponding to the slope of the PSD curve) and roughness parameters A_j (corresponding to the intercept of the PSD curve) were got from the logarithmic PSD curves. The relationship among D_j, A_j and the joint roughness coefficient (JRC) was studied, and the expressive forms of JRC with the new index were established. Meanwhile, the new index was extended to reveal the characterization of three-dimensional morphology, which was also used to calculate surface roughness of a marble surface obtained by the shear test. The results show that the new index has an extremely slight evaluation error, and can reflect the anisotropic property and effectively character morphology features of the structural plane, which provides a reference for characterizing the roughness of the structural plane and it is of great significance to study shear mechanical properties of the structural plane.

Concrete dam-foundation dynamic interaction plays an important role in the earthquake response analysis and safety assessment of the high concrete dam. Based on perfectly matched layer (PML) theory, the wave equation and finite element equation of perfectly matched layer artificial boundary in time domain are deduced and implemented. The accuracy and stability of PML artificial boundary simulation of far-field radiation damping is verified through the problem of wave absorption under the transient dynamic load. The reliability and validity of the ground motion input model based on PML artificial boundary is verified based on domain reduction method (DRM) and PML artificial boundary. A retaining dam section of a concrete gravity dam is considered. The results of PML artificial boundary and seismic input model, traditional massless foundation model and viscous-spring artificial boundary model are compared. It is found that the peak values of the horizontal and vertical relative displacement of the dam crest with the PML artificial boundary are reduced by about 40.6% and 31.7% when compared with those of the massless foundation model, and the relative peak displacements of PML artificial boundary are close to those of viscous-spring artificial boundary, which provides reference for analysis of dam seismic response and reasonable seismic input.

The shield method is commonly employed in the construction of urban subways, and the stability of the excavation surface is extremely important for the safety of tunnel construction. When constructing tunnels in submerged or water-rich strata, the seepage force is a key factor affecting the ultimate support force of excavation faces. Uncertainty of natural geotechnical material hydraulic parameters significantly impacts the seepage force near the face. Based on the classic limit analysis and the random field theory, the principle of effective stress in saturated soil is introduced, and the stochastic numerical limit analysis method considering the influence of pore water pressure is established by combining finite element spatial discretization and second-order cone programming. On this basis, the influence of spatial variability of permeability coefficient on the stability of shield tunnel face in water-rich strata is studied. The results show that the heterogeneity of the permeability coefficient leads to an increase in the pore pressure gradient at the face. The increase in the variation of permeability coefficient and the ratio of vertical to horizontal permeability coefficient significantly increases the support force required to maintain the face stability, and the effect of cross correlation coefficient and autocorrelation distance is relatively small. The present research can provide theoretical guidance for evaluating the face stability of tunnels in water-rich strata.

To analyze the coupling action of rock block, bonding layer and rockbolt, a three-dimensional refined numerical model of jointed rock mass anchorage system under constant normal stress was established considering the elastic-plastic behavior of rock block, the deterioration of tensile and compressive stiffness of bonding layer and the necking characteristics of anchor bolt. The joint surface morphology was established based on Barton's joint surface roughness. The reliability of the model was demonstrated by comparing with the experimental results first. Then, the effects of anchorage angle and joint surface morphology on the shear performance and the progressive damage behavior of each element were further analyzed. The results are summarized as follows: the deformation of rockbolt exhibits three stages: linear elasticity, plastic strengthening and ductile damage softening. The anchor angle has a great influence on the stress distribution, and the breaking displacement of rockbolt decreases with the increase of anchor angle. The horizontal displacement of rock block shows three stages: no obvious increase, slow increase and rapid increase. The roughness of joint surface greatly affects the morphology of plastic zone of rock block. The stiffness reduction trend of bonding layer exhibits a three-stage linear variation law. The bonding layer is prone to debonding due to extrusion, resulting in uncoordinated deformation of anchoring system. The conclusions are of great significance to the disaster prevention of anchorage engineering.

Submarine landslide is one of the main marine geological disasters. Once submarine slide happens, it will cause serious damage to underwater infrastructures. However, there are few researches on the movement and evolution of submarine landslides, especially considering the viscous effect of submarine landslides. A fluid-structure coupling model describing the interaction between water and particles was established by using computational fluid dynamics (CFD) and discrete element method (DEM), and a cohesive force model was introduced to develop a coupled CFD-DEM analysis method considering the viscous characteristics of sliding body. On this basis, the kinematic characteristics (velocity and distance) and morphological characteristics (length, width, shape, etc.) of the submarine landslide were systematically simulated by considering the viscosity and initial velocity of the landslide, and the influencing mechanism of the evolution process of the landslide movement was investigated in depth. The results show that the coupled method can simulate and reproduce the small-scale movement behavior of the submarine landslide well, the viscous action of the landslide has a remarkable influence on its kinematic and morphological characteristics, and the initial velocity also significantly affects the evolution and distribution characteristics of the particle flow field in each part of the landslide. The results can provide a scientific basis for the evolution process simulation and the effective prediction of submarine landslides.

Most soils in nature are unsaturated media, however, most of the soil was assumed to be elastic or saturated media in the previous studies on the transient dynamic response of circular lined tunnels. In this paper, considering the dynamic interaction between the soil and the tunnel lining and the additional mass density caused by dynamic load, the transient dynamic response of a deeply buried cylindrical lined tunnel with infinite length in saturated soil is studied. Based on the porous medium mixture theory and continuum mechanics theory, the controlling equations of the tunnel lining and unsaturated soil are derived when the cylindrical lined tunnel is subjected to transient load. The dynamic response of lining and unsaturated soil in time domain is obtained by using Durbin numerical inversion method. The effects of different saturation degrees on radial displacement, radial stress, hoop stress and pore water stress under transient load are presented and discussed. The results show that (a) the saturation degree has a significant influence on the transient dynamic response of lining and unsaturated soil; (b) the saturation degree has a less influence on the radial attenuation of radial displacement, but has greater influence on the radial attenuation of hoop stress and pore pressure.

In the process of mining in underground coal face, it is the guarantee of safe and efficient production of coal mine to grasp the abnormal situation in front of coal face in time. Ground penetrating radar (GPR) is an efficient and non-destructive detection method, which is widely used in mines. Significant achievements have been made in the image interpretation and imaging accuracy of GPR for detecting abnormal body response, but how to delineate the location and spatial distribution of geological abnormal body with GPR is a hot research issue. In this paper, a new method, which combines multiple sections and linear interpolation, is developed for accurate detection of abnormal body in coal mining face. The main research ideas are as follows. Firstly, forward simulation of 3D model of coal seam cavity and fault is carried out by using finite difference time domain algorithm (FDTD), and the response range of abnormal body is roughly delineated by Kirchhoff migration. Secondly, the multi-section view of single channel wave data with abnormal body response was obtained, and the exact position coordinates and specific dimensions of abnormal body were determined by linear interpolation, and the area evaluation criterion was introduced to verify the similarity of detection results. Finally, a GPR of LTD-2600 and a 900 MHz shielded antenna were used to conduct field experiments on the constructed physical cavity model, and the calculated cavity profile was compared with the actual cavity size for verification. The proposed method was applied in 18201 face of Xiegou coal mine to verify its validity. It is proved by practice that the error between the measured and actual spatial positions is less than 10%, and the specific size and spatial distribution range of abnormal bodies can be delineated relatively accurately.

The hydraulic conductivity function of unsaturated soil spans several orders of magnitude. Traditional measurement methods often take several months, and it is difficult to measure the hydraulic conductivity in the full suction range. In order to realize the rapid measurement of hydraulic conductivity in the full suction range, the wetting front advancing method is combined with the instantaneous profile method (here referred to as the combined determination method) in this study. A self-developed soil column infiltration device was used to measure the hydraulic conductivity of Qinghai silty clay in the full suction range under different dry densities. The test results show that in the combined determination method, the wetting front advancing method is suitable for the measurement of hydraulic conductivity in the high suction range (ψ > 25 kPa), while the instantaneous profile method is suitable for measuring the hydraulic conductivity in the low suction range (ψ ≤25 kPa). The hydraulic conductivity determined by the two methods in the overlapped suction range is basically consistent. The combined determination method can reduce the measurement time of hydraulic conductivity in the full suction range by about one week with good accuracy. In addition, the error sources of the two measurement methods are also analyzed and discussed in this work. The results show that the combined determination method can realize the rapid measurement of hydraulic conductivity in the full suction range, which is expected to make the measurement of the hydraulic conductivity of unsaturated soil become a routine test in soil mechanics.